Society and the Environment: Conserving Top Predators

Successful reintroduction of wild wolves in the American West has led to significant changes in the ecosystem.

Return of Wolves
By the early 1900s wolves had been virtually eliminated from most of their native range in the United States. They were hunted vigorously because they killed livestock. In Yellowstone National Park, wolves were hunted to extinction.

When the wolves disappeared, populations of elk—a favorite food of wolves—began to increase. As early as the 1930s, environmental scientists were worried that elk overgrazing was harming the park.

In 1995, the first wolves were reintroduced into Yellowstone, and their populations have been increasing in the park and other areas of the American West. In Yellowstone, wolf populations grew to over 170 animals, but subsequently declined to around 100. The population decline appears to be partially due to decreases in populations of elk—the favorite food of wolves. Elk also changed their behavior to stay safer from wolves. The return of wolves to Yellowstone has triggered other changes in the ecosystem. Plant communities changed in response to less grazing from elk. For example, willow trees near rivers have increased. Willow is a tree beavers need to survive the winter, so populations of beavers have increased. The beavers have changed streams and ponds, creating habitat for many other species.

Changes in ecosystems after the reintroduction of wolves have been so large that some scientists have suggested that predators should be reintroduced to more areas to improve ecosystem health.

Ocean Predators
While wolves are making a comeback on land, large predators in the ocean are in trouble. One example of ocean predators in trouble is sharks. Sharks are being overfished around the world, mainly to fill demand for shark fin soup. In many places, valuable fins are removed from the shark, and the rest of the body is thrown back into the sea. Tens of millions of sharks are killed each year. Unlike other fish, sharks take years before they can reproduce and they only have a few young each year. That means that they cannot survive heavy fishing. It is estimated that populations of sharks may have declined by more than 90% in some cases!

Should we worry about the disappearance of sharks? Recent studies say yes! Work in Western Australia by the Florida International University–led Shark Bay Ecosystem Research Project has shown that tiger sharks may be as important to ocean ecosystems as wolves are on land. By changing where and how marine herbivores like turtles and sea cows feed, tiger sharks protect seagrass. This seagrass is food and habitat for many species of fish and invertebrates, including many species people eat. Scientists also have found that having healthy shark populations is associated with healthy ecosystems in other parts of the world.

The impact of tiger sharks on ocean ecosystems is a subject of study for the Shark Bay Ecosystem Research Project in Australia.

People also have found out that living sharks are more valuable than dead sharks. Not only do living sharks help keep ecosystems healthy, but scuba divers will travel from all over the world to see them in their natural habitat. If there are enough sharks, each one may be worth more than $1 million in tourism over its lifetime!

Some environmental scientists and conservation groups are now trying to convince governments that sharks should be protected and efforts be made to help their populations increase where they have been overfished. Good science and economics have caused some governments to listen.

In some places, trade in shark fins is now illegal. In others, including the USA, sharks must be brought to shore with their fins attached. That means that fewer sharks can be caught on a single fishing trip. Also, species that are most in trouble are now protected in many areas.

In other areas, shark sanctuaries have been created. Inside these sanctuaries, no sharks can be caught and killed. Palau created the first shark sanctuary in 2009. Since then, Honduras, The Bahamas, the Maldives, Tokelau, and the Republic of the Marshall Islands have set aside huge areas of ocean as shark sanctuaries.

Environmental scientists are now studying how ocean ecosystems respond to the protection of sharks. Perhaps the same benefits seen on land with the return of wolves will occur in the oceans.

Ongoing Challenges
Even though things are looking up for wolves in North America and sharks in some places of the world, there are still major challenges. Throughout most of the world, predators on land are still in trouble. They are being killed because they eat livestock and their habitat is being destroyed. In the oceans, species of large sharks and other marine predators that may be among the most important to ecosystems can swim for thousands of miles. That means they often leave even large sanctuaries and can be caught in fisheries. Environmental scientists are working hard to understand these challenges and to find solutions that balance having healthy populations and ecosystems with people’s needs.